As for an electrophotographic photoreceptor (hereinafter, simply referred to as a photoreceptor), it is required to provide a predetermined sensitivity, electric properties and photo properties according to used electrophotographic process. Especially, as for a surface layer which is a farthest region from a substrate and is subjected to an electrical and mechanical force such as charging, exposing, transferring, or cleaning, it is required to provide a durability to maintain the above properties stably, even though image formation is carried out repeatedly. Specifically, it is required to provide enough durability to generation of an abrasion or scratch on a surface by rubbing and deterioration by ozone or nitrogen oxide generating at charging process.
From the background above, investigated were technologies which enhance a mechanical strength of photoreceptor surface by providing a surface layer. Specifically, investigated were technologies which enhance durability to an abrasion or scratch by increasing surface hardness of a photoreceptor (for example, Patent Document 1).
Further, investigated was technology which further enhances a mechanical strength of a surface layer by dispersing inorganic particles such as silica in a surface layer, as well as using a resin having a cross-linking structure (for example, Patent Document 2).
In this photoreceptor having a surface layer using a resin having a cross-linking structure, a mechanical strength of photoreceptor surface can be enhanced, but an electrical property on a photoreceptor surface is affected. Specifically, when an image was formed under an ambient of high temperature and high humidity, it was found that corona product such as ozone or nitrogen oxide which was generated by repeatedly charging, tended to adhere to a surface of a photoreceptor. These corona products adhered on a surface of a photoreceptor caused to decreasing a surface resistivity of a photoreceptor and resulted in a defect of an image such as blur.
Consequently, in a photoreceptor having a surface layer using a resin having a cross-linking structure, a balance between an electrical performance and a mechanical performance becomes problematic, because stable electrical performance tended to be difficult to be achieved when a mechanical strength was enhanced.
On the other hand, a need for balancing long life and high quality of an electrophotographic photoreceptor was increasing day by day, because in the market, there becomes a need for forming a lot of print more than one million papers scale by using an electrophotographic image forming apparatus.
Therefore, required was a photoreceptor which can have an excellent durability to generation of an abrasion or scratch on a surface by rubbing repeatedly in an image forming process and have an excellent charging potential property even when an image was printed repeatedly under an ambient of high temperature and high humidity.